A so-called brazed plate heat exchanger is a multilayer heat exchanger in which a plurality of heat transfer plates are stacked while being clamped between end plates provided on two sides and are joined into one plate by brazing. Adjacent heat transfer plates each have rows of channel forming patterns of projections and recesses formed on their continuous surfaces. Peaks of crests and troughs of the channel forming patterns on the adjacent heat transfer plates abut against each other to form interspaces serving as channels for fluid. Moreover, the abutting support points are joined and fixed by brazing. Each of the end plates has an inlet port and an outlet port for fluid serving as a heat transfer medium, and the heat transfer medium flows through the interspaces to exchange heat.
As the above-described channel forming patterns, a combination of adjacent V-shaped waves and inverse V-shaped waves is known as an example (see, for example, Patent Literature 1). A pattern formed by continuous waves orthogonal to each other is known as another example (see, for example, Patent Literature 2).
In a plate heat exchanger disclosed in Patent Literature 1, waves that form channels have a wave angle θ (inclination angle) of 20° to 70° (preferably 45°), a wave height h of 1 mm or less, and a wave pitch of 4 mm or less.
In Patent Literature 2, a hydraulic diameter Dh (=2×h) is 1 to 3 mm, and a wave height h is 0.5 to 1.5 mm.